A capsule significantly contributes to a microbe's pathogenicity by helping it evade the host immune system. It makes it considerably more difficult for phagocytic cells, such as white blood cells, to adhere to, engulf, and kill the microorganism, partly because the capsule physically enlarges the cell. For example, Streptococcus pneumoniae produces a capsule that is well known to aid in its virulence and ability to cause disease.